Industrial robots often employ an articulated mobile structure, commonly referred to as an arm, with mobility approximating that of a human arm. Such a robotic arm is equipped with a so-called end effector to enable the robot to perform its assigned task.
In some applications, the end-effector performs a grasping or gripping function. One class of gripping end-effectors uses a set of individual prehensile mechanical fingers (typically two or more) which curl around an object, tightening around it in order to grip the object. This action closely mimics the grasping action of the human hand.
A mechanically simpler gripping action can be obtained by employing an attractive force, such as a magnetic or electric field or fluid suction. The gripper is placed against the object to be grasped and the attractive force is energized (e.g., the magnetic field or suction force is turned on). The object is then grasped for subsequent manipulation. When the robot is finished with the object, the attractive force is turned off, and the object is released.
However, some objects to be grasped are bulky and/or offer no obvious flat space against which to exert an attractive force. Examples include paint brushes and many surgical instruments. If, for example, a conventional electromagnet is used to grip a metal surgical instrument, the pole piece of the electromagnet may rest against a high spot or sharp surface or other irregular surface on the instrument. When the electromagnetic field is energized, the resulting grip may be less than satisfactory and the object may dangle, twist, or even be dropped.